Methods and apparatus are known from the prior art in which grinding worms that are used at high to very high speeds can be dressed using a known and proven profiling process at low speeds and nevertheless have the required exact profile geometry at working speeds, i.e. in the stress condition under centrifugal force.
It is known that the measuring of the grinding worm profile can take place, for example, directly at the grinding worm by means of a contactless measurement system—such as laser optical distance measurement—or indirectly via the grinding and measuring of a sample workpiece. It is furthermore known here to measure the grinding worm profile at a profiled grinding worm that is slightly deformed due to the effect of the centrifugal forces at a working speed.
A multi-stage setting up process is required when setting up a gear cutting machine for machining precut gear workpieces. The geometrical dimensions of the tool first have to be manually determined outside the gear cutting machine or can also be taken from tool data sheets depending on the dimensions. These data subsequently have to be stored in the machine control. Some of these geometrical data change over the course of time with dressable tools—e.g. during dressing—such as the worm diameter or have to be additionally modified with a changed worm diameter to avoid profile errors such as applies, for example, to the lead or to the pressure angle. These data also have to be recorded over the grinding worm usage time so that they are available again on a repeat changing in of the tool.
In a further step in the setting up process, the location of the tool threads relative to the rotational position of the tool axis has to be stored in the control. This information and the position of the tool tooth spaces relative to the rotational position of the workpiece axis are required to be able to carry out an error-free, generator-coupled gear machining process. These further process steps are frequently called meshing.
In the subsequent machining process, only the location of the workpiece tooth spaces of each workpiece to be machined then has to be determined by means of a meshing sensor and the matching rotational position of the workpiece axis has to be stored. The rotational position of the workpiece axis is then synchronized with the rotational position of the tool axis in the machining process so that the tool threads can dip into the tooth spaces without collision and the workpiece can be machined in a generator-coupled manner.
To date, some of this total process is disadvantageously carried out manually or only semiautomatically despite the already highly automated gear cutting processes. The operator has thus previously had to position the tool relative to the tooth space of a workpiece during the first meshing after the substantially manual input of the geometrical parameters of the tool. For this purpose, the tool is manually rotated about its axis of rotation for so long until the teeth of the tool can dip into the tooth spaces without collision. The tool is subsequently delivered and a respective contact is established between the left and right tooth flanks of the tool by shifting or rotating the tool and the measured value for this is recorded. The tooth center position of the tool relative to the tooth space can be calculated from these contact dimensions and the rotational position of the tool at which it can dip into a known tooth space without collision can be determined therefrom.
All these manual worksteps bring about disadvantages such as increased dressing times and, due to the manual operation, possibly occurring incorrect settings of the gear cutting machine.
Only the measurement of the grinding worm profile shape has previously been known at the working speed of the grinding worm. What is not known, however, is using a contactless measurement system for determining various geometrical parameters of a tool having a machining region of worm thread shape. Tool parameters can be fully automatically determined and incorrect inputs can thus be prevented by the automated determination of the different geometrical dimensions of a tool which the gear cutting machine requires for the workpiece machining.
The tool can advantageously be a grinding worm. Other tools of similar design can, however, also be subjected to the method such as peel hobs when in so doing the special feature of the worm threads interrupted by the gashes are taken into account in the parameter determination.
It is therefore an object of the application to carry out a fully automatic determination of process-relevant geometrical parameters of the grinding worm, to determine an automated determination of the location of the worm thread position relative to the rotational position of the grinding worm about its axis and to enable an automatic meshing of the grinding worm in the gear teeth of a workpiece.
This object is achieved in accordance with the application by a method having the features including the automatic determination of at least one parameter of a grinding worm of a gear cutting machine, said method being including that at least one parameter of the grinding worm can be automatically detected and/or determined by means of at least one sensor.
“Parameter” can here be understood as different geometrical dimensions such as the worm diameter, the worm width, the lead angle and lead direction, but also the number of starts of the grinding worm. A “parameter” in the sense of the application can, however, also include other aspects.
The “meshing of the grinding worm” can mean that a so-called rolling engagement is realized between the grinding worm and a toothed workpiece. An exact positioning and alignment of the worm thread or, with multithread grinding worms, the worm threads of the grinding worm and relative to the teeth of the toothed workpiece are therefore an absolute necessity.
The basic requirement for the method is first a calibration process in which the exact location of the sensor with respect to the grinding wheel and its positioning within the gear cutting machine is determined and stored. This is in particular the case since the sensor cannot necessarily be arranged centrally with respect to the grinding worm or otherwise in a known or defined position and the method would thus not deliver any usable results with an unknown position of the sensor.
In accordance with the application, the parameters can thus be determined faster and more exactly in an automated manner. This method can likewise provide an inexpensive and grime-resistant possibility for determining the parameters of the grinding worm. This provides the advantage with respect to the initially described prior art that incorrect settings by the machine operator can be reduced and a faster tool change can likewise be realized.
It is furthermore advantageous that it is possible to react to temperature changes or temperature-induced changes of the gear cutting machine geometry and that object shifts, etc. can be detected by means of the sensor and can be compensated where necessary.
Advantageous embodiments of the application form the subject of the dependent claims.
In accordance with a first embodiment, the pitch, the module, the diameter, the lead and/or the location of the worm in the tool holder and its outer dimensions in the V direction can be determined by a calculatory processing of the detected and/or determined values.
In the method in accordance with the application, a calibration process can be carried out in a manner known per se where required to determine the location of the sensor with respect to the grinding worm and/or to the positioning within the gear cutting machine. The calibration process here means a step that could be carried out every time on the carrying out of the method in accordance with the application before the further steps or before the further step or that is alternatively carried out on a first carrying out of the method before the further steps and that can be omitted in following applications of the method. The location of the sensor with respect to its positioning within the gear cutting machine is inter alia determined in the calibration process. The sensor here does not have to be literally arranged within the gear cutting machine, but can rather only be part of the structure of the gear cutting machine and can thus, for example, be arranged at one of the outer sides of the gear cutting machine.
In a further embodiment, the grinding worm is moved to a predefined reference point, the alignment of the A axis to 0°, to determine the number of starts. A plurality of revolutions, in particular three revolutions, of the grinding worm about the B axis is thereupon subsequently detected by the sensor.
Provision can be made in a further embodiment of the application that at least one respective measurement is carried out by means of the sensor above and below the axis center of the grinding worm to determine the lead direction and/or that the grinding worm is rotated and the lead direction is determined by a mutual displacement of the sensor and/or of the grinding worm in the V direction. In the first-named variant, a measurement is, for example, carried out above and below the center and in particular spaced apart from the center of the grinding worm in an axial direction, with it being possible subsequently to calculate and thus fix the lead direction of the grinding worm in a calculatory manner by the determination of these two points on the grinding worm. In the second-named variant, the determination of the lead direction is carried out such that the lead direction is determined by means of a rotation of the grinding worm and of a simultaneously occurring relative displacement in a specific V direction. With a previously correctly assumed lead direction, the signal obtained remains constant since the sensor moves synchronously with the worm thread. The assumption of the direction can thus be confirmed. If the signal drops because the sensor has moved relative to the worm thread, a conclusion can be drawn from this that the lead direction was incorrectly assumed and the direction of movement of the sensor has to be adapted accordingly. The lead direction can likewise be accordingly determined by means of the sensor.
In accordance with a further embodiment, the grinding worm can be traveled along its longitudinal axis direction or V axis direction or V direction to mesh the grinding worm, with the position of the teeth along the V axis direction being determined by means of the sensor and the center position between two teeth being calculated or determined from this.
In accordance with a embodiment, the sensor can be an optical sensor, an inductive sensor, a capacitive sensor, or an ultrasound sensor and can work in an analog or digital manner. The combination of the different principles and, alternatively or additionally, an embodiment of the application with more than one sensor is accordingly conceivable, with the sensors also being able to be configured differently here. This provides the advantage that a respective sensor can be used in dependence on the material of the grinding worm to be detected and a variable embodiment of the method is accordingly possible.
In an embodiment, a determination of different parameters by means of the sensor is possible for the automatic meshing of asymmetrical profiles. This provides the advantage that the meshing of a grinding worm having an asymmetric worm profile can likewise be carried out automatically and reliably.
The application is further directed to a gear cutting machine for carrying out one of the aforesaid methods, wherein a sensor is provided for scanning a grinding worm.
Further features, details, and advantages of the application are explained with reference to the embodiment shown by way of example in the Figures.